This invention relates generally to image registration boards and spacers of the type used photomechanical platemaking, and particularly to those used in page makeup (stripping) and exposing plates, proofs, or contact prints utilizing a "step-and-repeat" registration system.
U.S. Pat. No. 2,983,049 to Andrisani discloses a system for accurately positioning one or more negatives, flats, screens, plates, or masking sheets, and repositioning those items relative to a fixed reference point (or to one another) in discrete repeating increments. The system comprises a ruled board having evenly spaced index holes aligned along the rulers, and registration pins which may be received within those index holes. This ruled board is commonly referred to as a "step and repeat board," and the current state of the art in construction of step and repeat boards is shown and described in U.S. Pat. No. 4,987,686 to Ternes.
FIGS. 18-27 of Andrisani '049 and FIGS. 4 and 5 of Ternes '686 show the structure of the registration pins in substantially the same form that they are currently used. Each spacer includes a thin metal plate or base that has either one or two bottom pins projecting downwardly and a single top pin projecting upwardly.
Normally, the rulers are divided into integer units with several increments representing common fractions of one unit. The center of each index hole is aligned with an integer unit value on the ruler. A registration pin may have its top pin aligned vertically with one of the bottom pins (or with a single bottom pin), in which case the top pin will be aligned along an major division or integer unit value of the ruler when the bottom pins are inserted into the index holes. Alternately, a registration pin having two bottom pins may have the top pin disposed a predetermined distance or interval between the two bottom pins (and therefore between two corresponding index holes), thus creating an offset for the top pin. Registration pins utilizing such an offset top pin are referred to as "spacers."
The top pins of the spacers are usually offset in increments equal to the minor ruler divisions. For example, if the ruler units were in inches, the spacer offsets would reflect each fraction between zero and one unit in 1/64", 1/32", 1/16", 1/10", 1/8" or 1/3" increments. A conventional step and repeat board could be used with a set having a plurality of several different 1/16" increment spacers, for example, the spacers in that set typically having offsets of 1/16", 1/8", 3/16", 1/4", 5/16", 3/8", and 1/241 relative to one of the bottom pins (and therefore a selected index hole.) The orientation of each spacer relative to a particular index hole can be reversed, thus permitting offsets of 9/16", 5/8", 11/16", 3/4", 13/16", 7/8", and 15/16" from the same set of spacers. The ruler units could be metric, points, picas, or any other convenient and uniform scale.
Currently, the common practice is to space the negative, flat, screen, plate, or masking sheet a short distance away from the ruler and spacer, and apply a paper or thin plastic stripping tab overlapping both the spacer and flat (as shown in FIG. 15 of Andrisani '049 and FIG. 1 of Ternes '686.) The stripping tab has one or more holes to receive the pin of the spacer, and the opposing end is taped or adhered directly to the negative, flat, screen, plate, or masking sheet.
Once the negative, flat, screen, plate, or masking sheet has been aligned or registered as desired using a registration pin or spacer, this particular registration may be accurately reproduced at the same location or anywhere along the ruler (or on a remote board or apparatus having a corresponding line of holes with or without a ruler) using either the same or a distinct set of negatives, flats, plates, screens, or masking sheets and a similar set of registration pins or spacers.
Page makeup may be done on a light table, step and repeat board, or similar layout device, and then subsequently transferred to the platemaker. The platemaker might be a vacuum frame, or an automated step and repeat registration machine. Factors affecting whether a vacuum frame or step and repeat machine is used in platemaking are discussed in the above referenced parent application Ser. No. 07/780,739.
Images (individual negatives or combined flats and any associated screens, plates, or masking sheets) may be transferred to an unruled image control board having spaced registration pins for exposure in a vacuum frame. It is known to provide the image control board with compressible registration pins, or in some cases the vacuum frames may have an integral registration system also including compressible registration pins. Compressible registration pins were similarly discussed in the above referenced parent application Ser. No. 07/780,739, with representative examples of compressible pins on image control boards and vacuum frames being shown in U.S. Pat. Nos. 4,977,683 to Harder and 3,634,009 to Van Dusen. Another alternative has been to equip the image control board or the blanket of the vacuum frame with an elastomeric cushion or substrate that supports the registration pin, and which deforms to simulate compression of the pin. A representative example of such a technique is shown in U.S. Pat. No. 4,636,067 to Richards.
However, the compressible registration pin and step and repeat (or image control) board disclosed therein are not completely suitable for all situations and applications, particularly those wherein a person would prefer or require the utilization of offset spacers to minimize the number of steps or transfers involved in the process of page makeup or the actual platemaking itself.
Some of the various deficiencies of these approaches found in the prior art have been discussed and addressed in the above referenced parent application Ser. No. 07/780,739, which discloses the structure, construction, and use of a compressible registration pin and step and repeat (or image control) board having the particular attributes and advantages disclosed therein.
Compressible spacers fabricated using molded plastic bodies and spring-biased metal posts are known to the art. One representative example of such a compressible spacer is manufactured by Stoesser Industries of Mountain View, Calif., doing business as Stoesser Register Systems. This compressible spacer is limited in that the body of the spacer is light weight and easily displaced from the registration board, if subject to weakening and deformation from high temperatures, can be cracked or broken by the heavy lid of a vacuum frame. In addition, the body defines a bore to receive the retractable post and compressible spring that extends entirely through the body. Consequently, the assembly requires a locking ring, washer, or crimped collar to retain a separate metal disk opposing the bottom of the retractable pin to present a surface from which the compressible spring can bias the retractable post upward, therefore requiring several manufacturing steps to assemble, and which can fail due to the stress of repeated use in normal operating conditions or higher temperature situations where the elasticity of the plastic body increases.